The present application relates generally to journal bearings for use in gearboxes and more particularly relates to a journal bearing design for facilitating hydrodynamic oil flow, bearing load capacity and optimization of bearing performance.
Gearboxes are used for power transmission in many systems such as, wind turbines, automobiles, aircraft and locomotives. A gearbox typically includes components such as a housing, shafts, bearings, and gears. Various gearbox designs are available to meet different speed transmission requirements. Of concern herein are epicyclical gear systems consisting of one or more outer gears, or planet gears, revolving about a central, or sun, gear.
Generally, epicyclical gearboxes are characterized as star-type, planetary type or differential type. In a star type gearbox, the carrier and bearing journal pin are fixed and the input torque/speed is through a sun gear shaft. The output torque/speed is through a ring gear and vice versa. In one particular example, it is known to use a star-type epicyclical gearbox in an aircraft to drive aircraft engine accessories in response to rotation of a rotor. It is also known that the planet gears of such a gearbox, are typically formed having a thin-rim. These thin-rimmed planet gears and the bearings associated therewith, are subjected to high loads and thus suffer from high rates of wear under such demanding usage and do not provide ready accessibility for the maintenance, repair and replacement of these key wear components. More particularly, analysis, testing and understanding of the behavior of a highly-loaded thin-rimmed planet gear in a planetary gearbox has revealed an undesired behavior in the form of high planet gear distortion that negatively influences the performance of a planet-pin operation and may lead to bearing seizure and failure.
Gears, bearings, and shafts in a gearbox may have defects, may fail over time, or may simply wear out. These damaged or worn components may be replaced after the damaged or worn condition is detected. However, taking a gearbox out of service for such replacement typically results in revenue loss. Any failure of individual components affects the residual useful life (RUL) of the gearbox. Of particular interest with regard to maintenance of star-type epicyclical gearboxes is the flow of hydrodynamic oil within the gearbox bearings, especially under high-load distortion instances, that serves to minimize or eliminate wear to the component parts. A lack of hydrodynamic lubricating fluid flow between the body of each of the bearings and the associated journal pin may result in a lack of lubrication within the bearing and planet gear that may result in direct contact between the journal pin and the journal bearing body. This direct contact may result in quickly wearing out the bearing, decreased load capacity and susceptible to seizure.
Accordingly, there is need for a new and improved epicyclical gearbox including a journal bearing, in which lubrication of the component parts, and in particular an improved flow of hydrodynamic oil is provided within the bearing in an attempt to minimize or eliminate wear and tear on the gearbox bearings.